Associations of bases, resulting from the combination of a lithium alkyl or aryl with an alkali metal amide or hydride, polymerization process in which they are used, and product obtained

ABSTRACT

The invention relates to new associations of strong bases, having the following general formula: 
     
         n&#39; RLi--n MZ 
    
     in which: n and n&#39; are the numbers of mols of each compound, R is an alkyl or aryl radical, M is an alkali metal chosen from amongst lithium, sodium or potassium and Z is a hydride or an inorganic amide, the ratio n/n&#39; being between 0.2 and 50. 
     It is preferred to use bases in which the metal of the alkali metal amide or hydride is potassium or sodium. These associations are formed very rapidly and can be applied to anionic polymerization, in particular of conjugated dienes, in a solvent of low polarity or an apolar solvent. 
     The polymers thus obtained contain a high percentage of 1,2 or 3,4 structures.

This application is a division, of application Ser. No. 340,078 filedJan. 18, 1982 now U.S. Pat. No. 4,435,312.

The invention relates to a new association of bases, resulting from thecombination of two strong bases, and to its application to anionicpolymerisation, in particular of conjugated dienes.

The increase in the basicity of alkali metal amides when they areassociated with alcoholates or with alkali metal salts, such aspotassium thiocyanate, is well known. The properties of these "complex"bases are illustrated by the following French Patents of the ApplicantCompany: Nos. 2,352,834 and 2,430,428.

Despite their remarkable properties, especially as regards the anionicpolymerisation of vinylic derivatives, these bases cannot easily be usedfor the polymerisation of conjugated dienes such as butadiene orisoprene. Moreover, it is impossible to form the same complex byreplacing the amides by alkali metal hydrides, which are bases ofsubstantially identical basic power.

Furthermore, it is known to use strong bases, such as lithium alkyls oraryls, as initiators for the anionic polymerisation of conjugateddienes.

However, when this anionic polymerisation is carried out in an apolarsolvent or a solvent of low polarity (n-hexane or toluene), this beingby far the most advantangeous solution, the stereochemistry of thereaction leads to 90% of the 1,4 structure and only 10% of the 1,2 or3,4 structures.

It is known that it is desirable to increase the percentage of vinyliclinkages in the polymer so as to increase the curing rate and improvethe mechanical properties of the polymers, in particular as regardstheir shock-absorbing capacity.

Thus, to overcome these disadvantages, it was proposed to carry out thereaction in the presence of tertiary amines such asN,N,N',N'-tetramethylethylenediamine. The properties of these complexes,known as Langer complexes, are illustrated by British Pat. No.1,051,269.

This solution, although advantageous on a laboratory scale, isnevertheless rather expensive from the industrial point of view.

One object of the invention is to propose a new association of twostrong bases, the basic power of which is greater than that of each ofthe two bases from which it is formed.

A further object of the invention is to apply these new associations tothe polymerisation of conjugated dienes, in particular in non-polarsolvents.

The association has the following general formula:

    n'RLi--nMZ

in which: n and n' are the numbers of mols of each compound, R is analkyl or aryl radical, M is an alkali metal chosen from amongst lithium,sodium or potassium and Z is a hydride or an inorganic amide, the ration/n' being between 0.2 and 50.

Amongst the alkyl or aryl radicals, the following radicals may bementioned without implying a limitation: methyl, ethyl, n-propyl,isopropyl, n-butyl, isobutyl, t-butyl, n-amyl, n-hexyl, n-octyl,n-decyl, 2-butenyl, cyclopentylmethyl, cyclohexylethyl,cyclopentylethyl, methylcyclopentylethyl, 4-cyclohexenylethyl,2-phenylethyl, 2-phenylpropyl, methylnaphthylethyl, cyclopentyl,cyclohexyl, methylcyclopentyl, dimethylcyclopentyl, ethylcyclopentyl,methylcyclohexyl, dimethylcyclohexyl, ethylcyclohexyl,isopropylcyclohexyl, 5-cyclopentadienyl, phenylcyclopentyl,phenylcyclohexyl, phenyl, tolyl, xylyl, ethylphenyl, naphthyl,methylnaphthyl, dimethylnaphthyl, ethylnaphthyl and cyclohexylphenyl.

The preferred alkyl radicals are those containing 2 to 8 carbon atoms,in particular the butyl radical.

The preferred aryl radicals are the phenyl or naphthyl radicals.

The alkali metal of the hydride or amide must preferably be sodium orpotassium, so as to create an advantageous cation effect. Sodium is thepreferred cation.

The inorganic alkali metal amides, like the alkali metal hydrides, arevery strong bases of substantially equivalent basic power.

In fact, on the basicity scale, the following compounds are indecreasing order:

    MH>MNH.sub.2 >φ.sub.3 COM>φ.sub.3 COM>EtOM.

However, the alkali metal amide is preferred because of thesubstantially superior results which are obtained with the latter asregards anionic polymerisation.

It must be emphasised that the alkali metal amides used in the inventionare inorganic and that the nitrogen atom is not substituted by anorganic radical.

Although the ratio n/n' can vary considerably, it is preferably eitherequal to or greater than 1 and more particularly between 1 and 25,especially because of the higher proportion of vinylic structuresobtained.

These associations are in the form of aggregates which can be isolatedperfectly from the medium in which they were formed.

It is clear that a well-defined product is therefore involved, not atransitory and unstable form of association. It has been possible tokeep these complexes for 15 days without their showing any deteriorationas regards their properties.

The measurement of the basicity which was carried out in an organicmedium for some of these associations showed that there was a totallysurprising synergistic effect.

The following basicity scale is obtained:

    RLi--MZ>MZ>RLi.

Without being bound by any particular theory, it may be considered thatthe aggregates are, for example in the case of the associationn-BuLi--NaNH₂, in the following form: ##STR1## and more generally:##STR2##

The formation of these associations is very rapid, and virtuallyinstantaneous, at ambient temperature, and this is an additionaladvantage of the invention.

It is necessary only to form the associations under an inert atmosphereand in the absence of moisture.

One process for obtaining the associations of the invention consists inreacting the alkali metal amide or hydride, undissolved or dissolved ina solvent, with the organometallic compound, the latter being introducedunder an inert gas or in vacuo. The reaction is very rapid at 25° C.

The reaction can also be carried out at a lower temperature. In thiscase, however, the complexing time is longer. On the other hand, at ahigher temperature, the reaction is instantaneous.

It is obvious that other processes can also be used, in particular byreversing the order of introduction of the reactants into the flask.

The solvents which can be used for preparing the initiators according tothe invention must be aprotic and can be polar, weakly polar or apolar.Polar solvents can be used provided that their structure does not makethem susceptible to the action of the associations according to theinvention. Thus, dimethyl sulphoxide (DMSO) and dimethylformamide (DMF)are degraded by the associations and must preferably be avoided.

However, these associations can be prepared very easily in an apolar orweakly polar solvent such as toluene or compounds containing double ortriple bonds, and this is another advantage of the invention.

This advantage is even clearer when these associations are applied toanionic polymerisation, and this application will be described below.

In fact, a particularly advantageous application of the bases accordingto the invention consists in using them as anionic polymerisationinitiators.

In this respect, it is appropriate to make a clear distinction betweenpure anionic polymerisation, which is involved throughout the followingtext, and anionic coordination polymerisation, which involves initiatorssuch as salts of aluminium, of antimony and of transition metals (forexample the so-called Ziegler-Natta bimetallic catalysts), and whichbears no relationship to the field of application of the invention.

The associations can be used to initiate the polymerisation of anymonomers capable of undergoing anionic polymerisation by the opening ofan ethylenic double bond or a heterocyclic ring, and amongst thesemonomers, there may be mentioned ethylenic monomers such as styrene ormethyl methacrylate, heterocyclic monomers, and dienes such as isopreneor butadiene.

These monomers are well known to those skilled in the art and aredescribed, in particular, in French Pat. No. 2,410,005.

However, these associations are particularly valuable for initiating theanionic polymerisation of conjugated dienes. In fact, the alkali metalamides or hydrides have an astoundingly marked activating power withrespect to lithium alkyls or aryls as anionic polymerisation initiators.This synergistic effect brings improvements as regards the reactionrate, the nature of the solvent which it is possible to use, and thehigher percentage of vinylic structures present in the final polymer.

On these last two points, which are particularly important, thefollowing fact must be clearly emphasised: lithium butyl exists in thehexameric form, which is inert as regards anionic polymerisation. When anon-polar solvent is used, this hexameric form is very slightly andslowly dissociated, which explains the structure of the productobtained. On the other hand, polar solvents, such as tetrahydrofuran(THF), dissociate the hexameric form very rapidly, and this permits thevery rapid action of the lithium butyl, in this case, and the vinylicstructure of the product obtained. Admittedly, the association of analkali metal amide or hydride with lithium butyl makes it possible todissociate the hexameric form and to lead to the same effect as THF,but, in addition, this effect is much more pronounced and the percentageof vinylic structures obtained is even higher, which illustrates the newfunction of the association. It is not therefore a simple dissociationof the hexameric form which is involved.

These bases also permit the synthesis of living polymers, andconsequently they are applied to the synthesis of block copolymers (forexample styrene/diene).

A second consequence is the proportionality relationship between thedegree of polymerisation and the monomer concentration. Thus, there is alinear relationship DPn=k(M), DPn being the number-average degree ofpolymerisation and being equal to (M)/(C), (C) corresponding to thecatalyst concentration and (M) being the concentration in amount ofmonomer. In this case, the molecular weight is proportional to theamount of lithium alkyl or aryl present. This property only applies tomonomers which do not polymerise directly with the alkali metal amide.

Although all the bases of the present invention are suitable forapplication to anionic polymerisation, it has been found that it isadvantageous to use bases in which the metal of the alkali metal amideor hydride is potassium or sodium. A very favourable cation effect isthus obtained. More particularly, it is very advantageous to use sodiumamide or hydride. ##EQU1## is between 0.2 and 50, preferably greaterthan or equal to 1 and more particularly between 1 and 25.

The process for carrying out this application consists in adding, to thepreformed base, the monomer to be polymerised, which may or may not bein a solvent. At ambient temperature, the reaction is instantaneous anda large temperature rise can be observed.

The solvent which can be used can be the same as that used for theformation of the bases according to the invention, but can also bedifferent.

It is obvious that one of the great advantages of the invention consistsin using non-polar solvents. The reaction temperature is preferablybetween -10° and +40° C. so as to obtain the maximum rate whilstavoiding side reactions.

The reaction is terminated by adding water or alcohol.

Analysis of the microstructure obtained shows that, for isoprene, theaddition has taken place in the 1,2- and 3,4-positions to an extent ofmore than 70% and even to an extent of more than 97% in the case ofNaNH₂.

The examples which follow illustrate the invention.

PREPARATION OF THE ASSOCIATIONS 1. Preparation of the association NaNH₂--BuLi

25.10⁻³ mol of NaNH₂ in 30 ml of toluene, and 6.10⁻³ mol of BuLi, areintroduced into a round-bottomed flask kept under an argon atmosphereand at ambient temperature. The reaction takes place in three minutesand a large temperature rise can be observed. The same procedure isfollowed with 2.10⁻³ mol of BuLi.

2. Preparation of the association NaH--BuLi

In the same manner as above, 25.10⁻³ mol of NaH and 35 ml of toluene areintroduced into a round-bottomed reaction flask, followed by 2.10⁻³ molof BuLi. The reaction takes place in three minutes at ambienttemperature.

3. Preparation of the association NaH--φLi

The final product is obtained by following the same procedure as above.

4. The following associations were also prepared:

    BuLi--KNH.sub.2 and BuLi--LiNH.sub.2.

5. The same products as those mentioned in the above examples areobtained under the same conditions, except that tetrahydrofuran is usedas the solvent.

ANIONIC POLYMERISATION 1. Polymerisation of isoprene by the associationalkali metal amide--lithium n-butyl

(a) These experiments are carried out with associations obtained with25.10⁻³ mol of alkali metal amide and 2.10⁻³ mol of n-BuLi in 35 ml ofsolvent.

10⁻¹ mol of isoprene is then introduced.

After a latency period of 10 minutes, the polymerisation takes placevery rapidly. The reaction is stopped after 15 minutes by introducingmethanol. The polymer formed is then precipitated in methanol, filteredoff and dried in vacuo. The yield is 100%.

The results, according to the solvents and bases used, are summarised inthe table below.

    ______________________________________                                               THF           Toluene                                                           % of    % of    % of  % of  % of  % of                               Association                                                                            1,4     1,2     3,4   1,4   1,2   3,4                                ______________________________________                                        n-BuLi   18      18      64    91     0     9                                 LiNH.sub.2                                                                    n-BuLi   33      28      39    49    16    35                                 KNH.sub.2                                                                     n-BuLi    9      23      68    17    27    56                                 NaNH.sub.2                                                                    ______________________________________                                    

(b) An experiment in 35 ml of THF with 3.10⁻² mol of isoprene, 2.10⁻³mol of n-BuLi and 25.10⁻³ mol of alkali metal amide gave the followingresult:

    ______________________________________                                        Yield   % of 1,4      % of 1,2 % of 3,4                                       ______________________________________                                        100%    6             30       64                                             ______________________________________                                    

(c) An experiment carried out under the same conditions as the precedingexperiment, but simply with n-BuLi, gave the following result:

    ______________________________________                                        Yield   % of 1,4      % of 1,2 % of 3,4                                       ______________________________________                                        100%    14            27       59                                             ______________________________________                                    

2. Polymerisation of isoprene by the associations NaH--n-BuLi andNaH--φLi

The procedure is the same as for Example 1. The associations areobtained with 25.10⁻³ mol of NaH and 6.10⁻³ mol of n-BuLi or φLi in 35ml of toluene.

10⁻¹ mol of isoprene is introduced.

The yield is 100% after 15 minutes.

The results are summarised in the table below.

    ______________________________________                                        Association  % of 1,4       % of 1,2 % of 3,4                                 ______________________________________                                        NaH--n-BuLi  34.4           11.4     54.2                                     NaH--φLi 27.5           16       56.5                                     ______________________________________                                    

3. Influence of the ratio sodium amide/lithium butyl for a given amountof sodium amide

    ______________________________________                                         ##STR3##    % of 1,4    % of 1,2                                                                               % of 3,4                                    ______________________________________                                        0.4         12          30       58                                           0.8         17          28       55                                           1.56        16          27       57                                           12.5        17          27       56                                           25          20          25       55                                           ______________________________________                                    

4. Comparison experiments

Under the same operating conditions which follow: 10⁻¹ mol of monomerand 6.10⁻³ mol of catalyst, the polymerisation of isoprene, initiated bylithium butyl and lithium phenyl, used without an activator, givespolymers with a different structure and a lower degree of conversion.

    ______________________________________                                                   Polymerisation     Structure                                       Initiator                                                                            Solvent   time        Yield  1,4 1,2  3,4                              ______________________________________                                        n-BuLi PhCH.sub.3                                                                              15 minutes  20     90  0    10                               PhLi   PhCH.sub.3                                                                              15 minutes  23     75  0    25                               ______________________________________                                    

5. Bulk polymerisation of isoprene

The association NaNH₂ --n-BuLi is prepared in toluene from 25.10⁻³ molof alkali metal amide and 2.10⁻³ mol of n-BuLi. The toluene is thenevaporated off.

10⁻¹ mol of isoprene is then introduced.

The following results are obtained:

    ______________________________________                                        Yield   % of 1,4      % of 1,2 % of 3,4                                       ______________________________________                                        100%    10            25       65                                             ______________________________________                                    

6. Polymerisation of butadiene with n-BuLi-NaNH₂

The experiments are carried out under the same conditions (2.10⁻² mol ofn-BuLi and 25.10⁻³ mol of NaNH₂).

    ______________________________________                                                 Reaction                                                             Solvent  time     Yield      % of 1,2                                                                             % of 1,4                                  ______________________________________                                        φMe  10'      100        86     14                                        THF      10'      100        90     10                                        ______________________________________                                    

A similar experiment, carried out in THF with n-BuLi by itself, andunder the same operating conditions, gives the following results:

Reaction time: 15 hours.

Yield: 100%;

% of 1,2: 77;

% of 1,4: 23.

7. Copolymerisation of styrene and butadiene with NaNH₂ --n-BuLi

5.10⁻³ mol of styrene (5 cc) is introduced into a round-bottomed flaskin which the association NaNH₂ --n-BuLi (respectively 25.10⁻³ mol and2.10⁻³ mol) has been formed in toluene. After a reaction time of 10minutes, 5.10⁻³ mol of isoprene is introduced.

After 10 minutes, the yield is 100% and the copolymer styrene/isopreneis obtained.

8. Polymerisation of methyl methacrylate by NaNH₂ --n-BuLi

In the same manner as for the preceding examples, 5.64.10⁻² mol of themonomer is added to the association prepared, in a solvent, from 25.10⁻³mol of NaNH₂ and 2.10⁻³ mol of n-BuLi.

The following results are obtained according to the solvents:

    ______________________________________                                         Solvent                                                                                 ##STR4##                                                                                    ##STR5##                                                                               I                                           ______________________________________                                        Hexane    29,000        52,000   1.8                                          Toluene   22,500        105,000  4.7                                          Dioxane   19,000        86,000   4.5                                          DME       32,000        85,000   2.7                                          THF       15,000        22,000   1.5                                          In bulk   21,000        15,000   7.1                                          ______________________________________                                         ##STR6##                                                                      ##STR7##                                                                      I: polydispersity index.                                                 

The following results are obtained according to the associations, theproportions of hydride and amide being identical.

    ______________________________________                                                   ##STR8##                                                                                  ##STR9##                                                                              I                                              ______________________________________                                        NaH--n-BuLi 19,000        170,000 8.9                                         NaNH.sub.2 --MeLi                                                                         94,000        510,000 6.9                                         NaNH.sub.2 -- Li                                                                          16,000         91,000 5.7                                         ______________________________________                                    

We claim:
 1. Process for the polymerisation or copolymerisation ofvinylic, heterocyclic or diene monomers capable of undergoing anionicpolymerisation by the opening of an ethylenic double bond or anheterocyclic ring, wherein said monomers are initiated, in the presenceor absence of a solvent, with an association of bases, of formula:

    n'RLi--nMZ

wherein n and n' are the numbers of mols of each compound, R is alkyl oraryl, M is sodium or potassium and Z is an hydride or an inorganicamide, the ratio n/n' being between 0.2 and
 50. 2. The process accordingto claim 1 wherein the monomer is a conjugated diene.
 3. The processaccording to claim 2 wherein the monomer is isoprene.
 4. The processaccording to claim 1 which is carried out in the presence of a solventwhich is apolar or weakly polar.
 5. The process according to claim 4wherein the solvent is the monomer to be polymerised.
 6. The processaccording to claim 1 wherein the polymerisation temperature is between-10° and +40° C.
 7. The process according to claim 1 wherein the base isformed from sodium amide and a lithium alkyl or aryl.
 8. The processaccording to claim 1 wherein the ratio n/n' is between 1 and
 25. 9. Theprocess according to claim 1 wherein the alkali metal M is sodium. 10.The process according to claim 9 wherein R is butyl napthyl or phenyl.11. The process according to claim 1 wherein the association of bases isNaNH₂ --n-BuLi, NaH--φLi, NaH--n-BuLi, nBuLi--KNH₂ or nBuLi--LiNH₂.